1. Field of the Invention
The invention relates to the field of methods and systems for asynchronous distributed control of multiple projector displays.
2. Description of the Prior Art
Plug-and-play projectors are known and are described by Ramesh Raskar from Mitsubishi Electric Research Laboratory (MERL), Boston in U.S. Patent Publications 2004/0184010 and 2004/0184011, which are incorporated herein by reference. Centralized techniques have been used until now when automatically calibrating (both geometrically and photometrically) large high-resolution displays created by tiling multiple projectors in a two dimensional array. A centralized server managed all the projectors and also the camera(s) used to calibrate the display.
Large high-resolution displays created by tiling multiple display units in a two dimensional array are used regularly for many applications like visualization, training, simulation and collaboration. Projectors are usually preferred over LCD panels in such applications since the bezels bordering the LCD panels make them incapable of generating one seamless image. However, projection based tiled displays suffer from two other problems as illustrated in FIG. 3c, namely the image is not geometrically matched across the projector boundaries; and/or the color and brightness of the image is non-uniform due to overlap in the projected area of adjacent projectors on the screen which appears doubly bright, and also due to varying color/brightness within and across projectors. In the early days of tiled displays, the prohibitive cost of projectors and driving engines limited the number of projectors to a handful allowing manual geometric alignment and color balancing of the display. With the advent of commodity projectors and PC clusters to drive them, displays with a large number of projectors are very affordable today.
But, manual calibration methods are both infeasible and unscalable for such large displays. So, several camera-based calibration techniques have been devised to calibrate these displays automatically, repeatably and inexpensively. All existing camera-based calibration techniques have a centralized architecture where one central machine or process bears the sole responsibility of achieving the geometric and color calibration by capturing specific projected patterns using a camera, analyzing them to generate the correction parameters, applying correction to different parts of the image to compensate for each projector's unique geometric and color artifacts, and finally shipping these images to the projectors to create a seamless display as illustrated in FIG. 1a. 
The advantage of centralized calibration is in having a common global reference frame to address the pixel geometry and color. Thus, managing multiple display units to create a global seamless image is relatively easy. However, centralized calibration is not scalable (increasing the number of projectors making up the display) or reconfigurable (changing the shape, aspect ratio and resolution of the display). Further, it is intolerant to faults, especially in the central server. In addition, deploying a centralized multi-projector display demands an educated user to set up the computers, projectors and camera appropriately, input the right parameters to the central server and maintain the whole set-up periodically.
Projectors today are affordable. Thus, building mammoth displays with billions of pixels by tiling hundreds of projectors is not unthinkable. At the other end of the spectrum, smaller, mobile and flexible “pack-and-go” displays are very much desired for applications like map and troop-movement visualization on the battlefield. They can even be used in public venues like schools and museums. A centralized calibration architecture inhibits the realization of the full potential of using projectors in these kinds of scenarios.